In recent years, with more and more needs of construction and maintenance for new energy projects such as large wind power equipment as well as construction for large petrochemical plant and power plant, the market for the automobile crane is quickly developed. In order to meet the requirements on the maneuverability and cornering behaviour of automobiles during short-distance site transfer or low-speed steering, the presently-produced automobile cranes with telescopic suspension arms or trussed suspension arms are generally provided with three or even more axles, and at least one rear axle of most of the automobile cranes is capable of active steering or follow-up steering.
For illustrative purposes, schematic diagrams of a three-axle all-terrain crane and a six-axle automobile crane are given. FIG. 1 is an all-terrain crane equipped with a hydro-pneumatic suspension, and FIG. 2 is an automobile crane equipped with a plate spring suspension. Either the all-terrain crane or the automobile crane may travel on construction sites and on public roads. Therefore, on the premise of satisfying the maneuverability of the automobile, all active steering rear axles must be controllable so as to prevent failures caused by a separated rear axle steering system.
With respect to an automobile crane similar to the ones shown in FIG. 1 and FIG. 2, rear axle steering may be realized by a mechanical steering linkage system or an electronic hydraulic steering device. For example, FIG. 3 is an example of a steering system for the all-terrain crane shown in FIG. 1, and FIG. 4 is an example of a steering system for the automobile crane shown in FIG. 2. In FIG. 3, the mechanical linkage connection to the front axle is cancelled. In FIG. 4, force transfer and steering transfer are transferred to the sixth axle from the first axle by a plurality of four-link mechanisms so as to obtain six-axles steering.
When the all-terrain crane shown in FIG. 1 adopts the steering system shown in FIG. 3 and normally travels on a road, the rear axle is kept at the middle position by a steering locking device mounted on the real axle, thus ensuring the straight travelling of the rear axle. The steering of the rear axle is only activated in a short time during transfer on a small site. That is to say, according to the steering technology shown in FIG. 3, the rear axle is incapable of active steering.
When the automobile crane shown in FIG. 2 adopts the steering system shown in FIG. 4, the rear axle is constrained by steering levers and only capable of reversely steering by following the front axle. The steering system shown in FIG. 4 has the defects that: too many steering four-link mechanisms are provided; transfer of the force and steering movement has to be determined according to the specific stiffness of the steering system, and the higher the stiffness of the steering system is, the faster the transfer speed of the force is, and the faster the rear axle steering is; after being used for a period of time, ball at both ends of a steering linkage assembly are worn, gaps are increased, the steering lag of the rear axle is increased, and abnormal wear of tires also occurs to a certain extent.
Some rear axle electronically-controlled steering systems and methods for an automobile crane also exist in the prior art, but are expensive and are not suitable for an automobile crane or an all-terrain crane with only one active steering rear axle, or not suitable for an automobile crane with a high travelling speed. Therefore, a novel follow-up steering control system is needed.